Thermionic tube



. Dec. 8, 1936. H. w. PARKER ET AL THERMIONIC TUBE Filed May 20, 1956 llE- l INVENTORS h @t Y. %m A m &/ B

Patented Dec. 8, 1936 UNITED STATES PATENT OFFICE THERMIONIC TUBE Canada Application May 20, 1936, Serial No. 80,728

7 Claims.

Our invention relates to thermionic tubes and pertains particularly to the structure and assembly of the electrodes in such tubes, especially of the type employing indirectly heated tubular sleeve cathodes.

The tendency in the last few years in the design of thermionic tubes has been to reduce the over-all dimensions and crowd into such reduced space more and more electrodes. This has resulted in reducing the spacing between the electrodes to such small dimensions that any variation, even very slight, in the relative positions of the electrodes represents a relatively large percentage of the total space between the electrodes and causes, especially in variations in the relative distance between the cathode and grids, what are known as tube noises. Spacers of mica have been almost universally used to support the electrodes and maintain the relative positions thereof, but recently spacers of refractory insulation material such as ceramic have been used in lieu of mica. The use of ceramic spacers has been found'to be advantageous because such spacers can be more completely freed of gas and have a better high frequency characteristic in providing a higher input impedance for the tube than can be obtained through the use of mica. The use of such ceramic spacers involves the serious problem of securing a rigid union between the spacer and the cathode and between the other electrode supports or standards, especially those supporting the grids and the spacer to avoid relative motion and consequent noise. For structural strength the ceramic spacers must have considerable more thickness than mica spacers and the area of contact between the cathode sleeve and the spacer is therefore much greater. This greater contact between the cathode sleeve and the spacer increases thermal conductivity between the sleeve and spacer and the spacer acts as an eflicient radiating vane to conduct heat away from the cathode sleeve and render the cathode less efficient and effective as an electron emitter. Various expedients have been resorted to in order to overcome this particular difficulty but none so far have been completely effective.

One of the principal objects of our invention comprises producing a simple and inexpensive thermionic tube structure employing spacers of refractory insulating material in which the electrodes are rigidly maintained in their proper relative positions in order to provide a noise free tube.

Another object comprises producing a thermionic tube structure employing spacers of refractory insulating material in which the cathode is rigidly supported yet in such manner as to ensure minimum thermal conductivity between the cathode and the spacer.

A further object comprises producing a thermionic tube structure in which the cathode is supported by a spacer of refractory insulating material through line contacts therewith only, in order to provide minimum thermal conductivity between the cathode and the spacer.

A still further object comprises producing a thermionic tube employing spacers of refractory insulating material with the spacers so made as to provide a high resistance path between the cathode and grid rods to increase the insulation resistance between the cathode and the grid and thus reduce leakage due to film of active materials sputtered on to the spacer.

We accomplish all of the above noted desirable results and others which will hereinafter be apparent by means of the novel structures, combination, inter-relation and arrangement of parts which will be hereinafter more specifically described with reference to the accompanying drawing forming a part of this specification and in which like numerals designate corresponding parts throughout.

In the accompanying drawing:

Fig. 1 is an enlarged sectional elevation of a simple triode incorporating our invention with the enclosing envelope broken away;

Fig, 2 is a greatly enlarged, partially broken and. sectioned elevation showing the details of the connection between the cathode, grid rods and spacer;

Fig. 3 is a plan view of a portion of the same; and

Fig. 4 is a greatly enlarged broken sectional elevation of the tool as used in expanding the cathode sleeve.

While our invention is, as hereinbefore stated,

especially advantageous for use with modern tubes of the multi-grid type, we have chosen, by

way of example only and for purposes of simpliclty, to illustrate our invention as used in connection with a simple triode.

Referring now to the drawing, and especially Figs. 1, 2 and 3, the electrodes are supported by the usual press and stem l to which the enclos-.

ing envelope 2 is attached. The anode I3 is supported by means of standards 4 and l which are in turn supported by the press I and one of which,

4, functions as the anode terminal. The grid I2 is supported on the grid standards 5 and 6, one

thereof. 1 the expanding mandrel is not only split but proof which, 6, is welded to a terminal standard 19. The cathode 3 is of the tubular sleeve type with internal heater as shown and is supported at the top thereof by the spacer of ceramic or other refractory insulating material 8. The ceramic spacer 9 serves to position the lower extremities of the electrodes as shown. Both the spacers 8 and 9 are provided with bosses l6 and [1, re-

spectively, provided with substantially centrally I, located apertures therein through which the cathode sleeve extends. The sleeve of the cathode 3 is expanded at its upper extremity as shown in Figs. 2 and 3, as "will hereinafter be described, to effect a rigid connection between the spacer 8 and the cathode. The grid standards 5 and 6 are cemented as shown in Figs. 1 and 2 by means of any well-known ceramic cement Il and I5, respectively. The apertures in the spacer 8 through which the grid standards 5 and 6 and anode standards 4 and I extend are as shown of larger diameter thanthe standards so that the cement l4 and I5 may enter the apertures and surround the standards to'provide a secure and rigid connection between the standards and the spacer. The spacer 9 is held in operative position by means of extrusions or pinches as l8 and 22 on the anode and grid standards as shown. Thelower end of the cathode 3 is held immovable by means of the stiff pigtail it) which is welded to the cathode terminal standard ll held securely in the press I.

Referring now particularly to Figs. 2, 3, and 4, the cathode is expanded by means of an expanding mandrel comprising the female member 3| and male member 30. The female member is introduced into the cathode as shown in Fig. 4 and so positioned that when expanded by the intro 'duction of the male member 30, arcuate ridges Y20 and 2| are bulged out, as shown in Figs. 2 and 3, to make a rigid connection between the spacer 8 and the cathode by line contacts therewith. It will be noted that as the female member 3| of the expanding mandrel is split in one plane only, the

introduction of the male member expands the mandrel to produce an oval contour for the sleeve of the cathode 3 as shown in Fig. 3. The arcuate ridges 20 and 2! therefore make contact with the upper and lower edges of the aperture in the spacer 8 only for about 90 degrees of the circumference of the aperture in the spacer. Thus there are only four 90 degree line contacts between the cathode and the spacer, or, in effect, a single circumferential line of meeting between the cathode and the spacer, thus providing a minimum opportunity for thermal conductivity between the cathode and the spacer. Further, the boss. IS on the spacer 8 serves to increase the thickness of the spacer at the point of meeting between the cathode and the spacer, thus ensures rigid connection between the cathode and the spacer and provides a high resistance path between the cathode and the grid standards to increase the insulation resistance between the cathode and grid and thus reduce leakage due to film of active ma- ,terials which may be sputtered on to the spacer in the fabrication of the tube or in subsequent use Preferably, the female member 3! of vided with a central tapered hole which centers and guides the male member 30.

While, we have shown in Figs. 2 and 3 greatly enlarged views of the manner in which the grid rods 5 and'ii arecemented into the spacer 8, it is to be understood as shown in Fig. 1 that the standards 4 and I for the anode l3 are similarly cemented.

Preferably the aperture in the boss H of the lower spacer 9 through which the cathode 3 extends is given a diameter to afford suflicient clearance between the cathode and the spacer to allow free thermal expansion of the cathode.

While we have described our invention in connection with a tube employing a vitreous press .tained in their proper relative positions in order to provide a noise-free tube, and that the cathode is rigidly supported yet in such manner as to ensure minimum thermal conductivity between the cathode and the spacer; that the cathode is supported by, so far as thermal conduction is concerned, in effect a single circumferential line contact between the cathode and the spacer to provide minimum thermal conductivity between the cathode and the spacer; and it will be further apparent that the bosses or annular shoulders on the spacers provide a high resistance path between the cathode and the grid standard to reduce leakage due to film of active materials sputtered on the spacer because of the surface discontinuity provided by the annular shoulders. It will be further obvious that our construction is simple, inexpensive and well adapted to mass production.

While we have shown and disclosed, by way of example only, one embodiment of our invention, it will be apparent that various changes may be made therein without departing from the intended scope and spirit of the invention. We do not therefore desire to limit ourselves to the foregoing except as may be pointed out in the appended claims in which we claim:

1. In a thermionic tube, a plurality of electrodes including a grid, acathode of the tubular sleeve type and an enclosing envelope therefor, spacers of refractory insulating material for maintaining the relative positions of said electrodes, one of said spacers acting as a support for said cathode and said cathode being rigidly secured in an aperture in said spacer through line contacts with a portion only of the upper and lower edges of said aperture.

2. In a. thermionic tube, a plurality of electrodes including a grid, a cathode of the tubular substantially rigidly secured in the aperture in said spacer through line contacts with a portion only of the edges of said aperture.

3. In a thermionic tube, a plurality of electrodes including a grid, a cathode of the tubular sleeve type and an enclosing envelope therefor, ceramic spacers for maintaining the relative positions of said electrodes, one of said spacers being provided with an aperture and acting as a support for said cathode, the sleeve of said cathode extending through said aperture and being provided with arcuate ridges near the upper and lower surfaces of said spacer to provide a substantially rigid connection between said cathode sleeve and spacer through line contacts between said arcuate ridges and the upper and lower edges of said aperture.

4. In a thermionic tube, a plurality of electrodes including a grid, a cathode of the tubular sleeve type and an enclosing envelope therefor, ceramic spacers for maintaining the relative positions of said electrodes, said spacers being provided with apertures through which the cathode and the standards supporting said electrodes pass, one of said spacers acting as a support for said cathode, the sleeve of said cathode being bulged outwardly to provide arcuate ridges near the upper and lower surfaces of said spacer to provide substantially rigid connection between said cathode sleeve and said spacer through line contacts with the upper and lower edges of the aperture in said spacer through which said cathode sleeve extends, and the supporting rods for said other electrodes being cemented in said spacer by means of a ceramic cement.

5. In a thermionic tube, a plurality of electrodes including a grid, a cathode of the tubular sleeve type and an enclosing envelope therefor, upper and lower ceramic spacers for maintaining the relative positions of said electrodes, said upper spacer being provided with apertures through' which said cathode and the supporting standards of said other electrodes extend, said cathode being substantially rigidly secured in said upper spacer by means of arcuate ridges formed therein to make contact with a portion only of the edges of the aperture in said upper spacer through which said cathode extends and the standards supporting said other electrodes being rigidly secured in the apertures in said upper spacer by means of a ceramic cement.

6. In a thermionic tube, a plurality of electrodes including a grid, a cathode of the tubular sleeve type, and an enclosing envelope therefor, ceramic spacers for maintaining the relative positions of said electrodes, said spacers being each provided with apertures annularly shouldered to increase the thickness of the spacers near said apertures, one of said spacers acting as a support for said cathode and the sleeve of said cathode extending through the aperture therein and being secured to said spacer by outwardly extending arcuate ridges formed therein to provide line contacts between said cathode and portions of the edges of said aperture.

7. In a thermionic tube, a plurality of electrodes including a grid, a cathode of the tubular sleeve type and an enclosing envelope therefor, ceramic spacers for maintaining the relative positions of said electrodes, one of said spacers being provided with a boss and a centrally located aperture therein and acting as a support for said cathode, the sleeve of said cathode extending through said aperture and being provided with arcuate ridges near the upper surface of said spacer and the lower surface of said boss to provide a substantially rigid connection between said cathode sleeve and spacer through line contacts between said arcuate ridges and the upper and lower edges of the aperture in said spacer.

HENRY W. PARKER. NORMAN A. YORKE. 

